The present invention relates to an arrangement and a method for dynamic control of the movements and course of a high-speed vessel hull. The invention consists in that movable flap members are arranged at one or more transitions between the stern of the vessel and aft side portions of the vessel so as to be capable of being moved out in the lateral direction of the vessel hull and in this connection generate force components which act essentially in the lateral direction of the vessel hull. The invention also relates to a method for dynamic control of the movements and course of a high-speed vessel hull.
The invention is intended in particular for manoeuvring vessel hulls of high-speed vessels of the type which are provided with water-jet drive, that is to say vessels with a water-free stem while in motion. Examples of such vessels are passenger ferries of single-hull or multi-hull type.
The invention can, however, also be applied to other types of high-speed vessel than passenger ferries, and also to smaller high-speed boats if desired. It is also possible to use the invention for vessels or boats which are driven in other ways than by water-jet units.
The use of high-speed vessels for more efficient transport of cargo, vehicles and passengers has today become increasingly widespread. A common type of such high-speed vessel is passenger ferries of the single-hull or catamaran type, which are often driven and steered by means of what are known as water-jet units.
It is previously known that high-speed vessels of the type in question can be associated with certain problems, such as pitching and rolling tendencies and also difficulties in maintaining the correct floating position while in motion. A contributory cause of such problems, for example with regard to passenger ferries, is that the load distribution between different journeys and/or trips can vary greatly depending on the number of cars and passengers and their positioning on board.
Various arrangements, such as hydrofoils and trimming flaps, which strive to counteract pitching and rolling tendencies and to maintain the correct floating position of the vessel hull while in motion, have therefore been known for a long time.
In this way, SE-C2-502 671 describes an arrangement for a planing or semi-planing vessel hull for trimming the floating position of the hull while in motion. The arrangement described in SE-C2-502 671 comprises a flap introduced, directly behind the bottom of the hull, into the relative water flow and transversely thereto to generate an eddy with an upwardly and forwardly directed force component in front of the flap, as a result of which a volume of water of increased pressure is created, which acts against a zone of the bottom of the vessel in front of the flap. The flap of the arrangement described is continuously adjustable to suitable depth by means of movement-transmitting members and vertically displaceably mounted in the lower edge of the stem of the hull. The arrangement described in SE-C2-502 671 is said to make possible continuous dynamic trimming of a high-speed vessel hull to counteract rolling and pitching movements while in motion. Different embodiments of the arrangement described are said to be capable of replacing either a movable trimming foil, a rigidly arranged trimming foil, or a wedge arranged below the aft part of the bottom.
A specific problem associated with modern high-speed vessels of the type which is usually operated by water-jet drive is that they tend to not have very good course stability. In the case of heavy seas from the stem, there is a certain risk that the manoeuvrability will be lost momentarily and the bow of the vessel will veer out to one side from the intended course (broach).
A previously proposed solution to this problem is to use keels, centre-boards and other xe2x80x9cdrift-brakingxe2x80x9d arrangements, with the aid of which it is possible to bring about better course stability. However, such previously known arrangements result in increased water resistance which leads to either a reduction in speed with maintained shaft power or increased fuel consumption at maintained speed because the shaft power must be increased in order to compensate for the increased resistance. Furthermore, such previously known arrangements for increasing course stability in general make manoeuvring of the vessel in the lateral direction more difficult.
Steering of waterjet-driven vessels is effected by controlling the direction of the water jet using course-changing means in the form of rotatable nozzles and/or rotatable shutter-like or scoop-like members. The dimensions of these course-changing means must be adapted so as to provide sufficient course-changing effect both at low speeds, such as when the vessel is within a harbour area, and when travelling at full speed. A certain xe2x80x9coverdimensioningxe2x80x9d is necessary then so as to ensure sufficient course-changing capacity in all possible situations. It is therefore not desirable to improve the course stability unilaterally at the expense of the manoeuvrability of this type of high-speed vessel.
A first object of the present invention is therefore to provide an arrangement for dynamic control of the movements and course of a high-speed vessel hull, which arrangement improves both the course stability and the manoeuvrability and also counteracts pitching and rolling tendencies of a high-speed vessel hull without resulting in any losses in speed.
This object is achieved by means of an arrangement, which comprises propulsion members and at least one flap member which is arranged so as to be capable of being brought adjustably at an angle in relation to a water flow relative to an aft side surface of the vessel hull in order in this connection to generate force components acting on said vessel hull and on a front side of said flap member, which side faces towards the water flow. According to the invention, the flap member is arranged so that, when the movements and/or course of the vessel hull change(s), the force components generated are directed on the one hand towards the aft side surface of the vessel hull and on the other hand towards the front side of the flap member in the water flow relative to the aft side surface.
A further object of the invention is to provide an improved method for dynamic control of the movements and course of a high-speed vessel hull. This object is achieved by means of a method, which comprises use of propulsion members and flap members with a front side. At least one flap member is at least partly introduced, while the vessel is in motion, into a water flow relative to the vessel hull, with the front side facing towards the water flow in order to generate force components acting on the vessel hull and on the flap member, the water flow comprising a volume of water below a water surface and the volume of water being under pressure. According to the invention, the flap member, when introduced into the water flow, increases the pressure of the volume of water, the increased pressure giving rise to the force components which are directed on the one hand towards the aft side surface and on the other hand in the direction of the front side of the flap member introduced.
Compared with the previously known technique of improving dynamic control of the movements and course of high-speed vessels, a number of advantages are achieved by means of the present invention, such as reduced energy losses and reduced loads on, for example, a waterjet unit because this can be kept in a xe2x80x9cfixedxe2x80x9d position and does not have to be used to steer the vessel while travelling at high speeds.
By virtue of the invention, the conventional steering, reversing and manoeuvring equipment of the vessel has to dimensioned only for travelling at low speeds. In the case of water-jet drive, the conventional system of steering the vessel is used only at speeds below around 15-20 knots, while the water-jet unit only functions as a propulsion unit at higher speeds.
The invention also makes possible a dynamic control/adjustment which results in smoother motion and which can take account of and counteract rough seas, and a reduced water resistance against the vessel hull which can lead to significant savings in terms of fuel or, alternatively, time. By virtue of the dynamic adjustment/control, the invention makes it possible for the vessel to travel at higher speed in, for example, heavy seas.
The control can also be based on various xe2x80x9ccomfortxe2x80x9d-related parameters so that the passengers on the vessel experience smooth motion with a high degree of comfort even in rough weather.
The invention also provides increased safety because it allows maintained controllability of the vessel even if, for example, a water-jet unit should break down while travelling at high speed.
Advantageous embodiments of the invention emerge from the dependent patent claims below.